It has been proposed heretofore to provide so-called universal or radial-jaw chucks with a common tightening member which can be axially displaced by a draw bar or tube running through the hollow spindle of the turning machine on which the operating mechanism may be provided at the remote end of the hollow spindle to pull a draw bar through the latter and thereby tighten the jaws of the chuck against their workpiece.
To this end, the chuck body which is mounted on the proximal end of the hollow spindle, can be formed with a plurality of angularly equispaced radially displaceable jaws which are urged toward the workpiece to grip the same or away from the workpiece to release the latter.
In prior-art systems of this type, the central tightening member is axially displaceable and cooperates via inclined teeth with the meshing or interdigitating teeth of a rack formed on the back of each of the chuck jaws.
This system has been found to have the disadvantage that it applies a torque or torsional stress to the tightening body and requires complex means for preventing rotation thereof. Nonetheless, when the tightening body is a tube, some mechanical distortion must be contemplated.
To prevent such torsional stresses from arising or to take up the torsional stresses and insure effective guidance or resistance to rotation, the chuck body must be modified in a manner which tends to weaken it.